Code a eftpos machine + Give advice

Square Reader In 2010, the Square device communicated with the Square app through a phone's audio jack. The Square Reader was the first product released by Square. It is used to accept credit card payments by connecting to a mobile device's audio jack. Square's original reader consisted of a simple read head directly wired to a 3.5 mm audio jack, strong encryption on its devices, including SSL and PGP.[9] Its cryptographic keys are at least 2,048 bits in length.[9] Neither card numbers, nor magnetic stripe data, nor security codes are stored on Square client devices.[9] Square follows the guidelines issued by OWASP.[9] accept chip cards and contactless cards. This new reader supports chip-and-signature and contactless transactions, and the standard Square Reader is also provided in order to support traditional magnetic stripe card transactions.[12] Accepting Apple Pay and other contactless payments, in addition to EMV chip cards.[13]